1. Technical field
The present invention is directed to a signal processor for selectively processing a plurality of signals. In the preferred embodiment, the signal processor selectively combines and averages random, non-periodic, low-level signals mixed with very high-noise contamination based on logic (selective weight) averaging.
2. Background Information
In many signal processing applications, it is frequently necessary to detect and process signals where the noise component is significant in comparison to the signal's information component. In fact, in many such noise contaminated environments, the noise component itself is larger than the information component. This very often occurs when the signal's amplitude is low and noise contamination will statisically be larger than information amplitude.
For example, electrical signals are generated as a result of the conduction system of the heart of the human body. These electrical signals have very small amplitudes and are ordinarily not detectable by the usual detection means of a simple amplifying circuit due to the magnitude of inherent environmental noise. This problem occurs in other small-amplitude information, high-amplitude noise environments, such as detecting other small-amplitude biological signals, such as those arising from the central nervous system, as well as signals in the field of space exploration, sound engineering, electron spin resonance devices, photochemical measurement, communication systems, and the like.
A number of different techniques are known in the art for reducing noise in low level signal measurements. In U.S. Pat. No. 3,126,449 issued to J. Shirman on Mar. 24, 1964, a noise discriminator circuit is shown having a logic circuit for opening a gate to pass the input signal in the event that the input signal has certain frequency characteristics. The logic circuitry includes a plurality of parallel channels for passing signals having the selected frequency characteristics and logically combining these signals to open the gate to pass the input signal. As a result, this circuit selectively discriminates against input signal noise of certain frequencies outside of the pass band.
Parallel input analog averaging techniques are also known in the art, as shown in U.S. Pat. No. 4,300,101 issued to the same inventor as the present invention, and incorporated herein by reference. In this patent, several parallel input signals are combined in an analog averaging circuit which utilize an analog averaging technique. This combined signal is fed through a variable gain amplifier, amplified, and output only in the event that the instantaneous polarity of all of the parallel input signals have the same value. In other words, only when all parallel input signals are either positive or negative will the input signals be averaged, amplified, and output. Such a circuit is shown to yield a signal amplification of N (the variable gain amplifier's gain factor) and a noise amplification of only the square root of N. As N is usually a very large number (i.e., 10,000), signal output is significantly higher than noise output, and thus the signal-to-noise ratio is significantly enhanced.
However, the problem with the analog averaging technique is that, in order to realize significant signal-to-noise ratios, a large number of parallel inputs must be used. This not only increases total system cost, but also degrades the overall performance of the system. Degradation occurs because, as more parallel inputs are added, the chances of all of the input values being mutually coincident statistically decreases. As coincidence is the criteria for signal output, a statistically lower number of signal averages will be output, thus reducing overall performance.